Ballistic Missile Defense has been set as a national priority for the Department of Defense. IR focal plane arrays (IRFPAs) are needed for ballistic missile defense (BMD), as well as many other military systems. BMD IRFPA applications extend from surveillance using ground, airborne and space-based platforms, to both endo- and exo-atmospheric interceptor seekers. Even though IRFPAs using material systems, such as HgCdTe and InSb, are adequate for most tactical military applications, certain IR systems for BMD exert a much more stringent requirements. For example, when IRFPAs are used in a system where the target is very cold, the background noise is orders of magnitudes lower than tactical scenes. In this case, the total noise of the IRFPA is dominated by the internal detector noise. With a cold dim target at a far away distance, IRFPAs with extended wavelengths are needed to receive as many photons as possible. The requirements of BMD IRFPAs with high sensitivity, large format, small pixel size and high frame rate, plus long cutoff wavelength and operating at low temperatures presents great challenges to IRFPA technology. Multi-color FPAs and active/passive fusion can greatly enhance the important task of discrimination and aim point selection.